Chairs or spacers are commonly used in the construction industry for the support and positioning of post-tension cables and/or reinforcement bars (“rebars”) a proper distance above a surface. The bars or cables are usually arranged in rows or grids within an area into which concrete is to be poured. They are held loosely in place while concrete is placed around them. In normal use, a receiving area formed on the chair will contact and support the cable or bar while the base of the chair rests on a deck or on a grade.
Post-tension cables differ from ordinary rebars in that they are high tensile strength steel cables that are pulled tightly after the concrete is poured. The reinforcing cable or tendon is stretched by hydraulic jacks and securely anchored into place just after the concrete is poured. When the concrete has set, it holds the steel in a tight grip, preventing slippage or sagging. Proper spacing and arrangement of post-tension cables, as well as rebars, according to known engineering and architectural specifications, impacts the structural strength and integrity of the concrete structure. Additionally, proper spacing of the bars away from the outer surfaces of the concrete structure helps prevent moisture from reaching and deteriorating the bars.
Various U.S. and foreign patents have issued on devices relating to chairs. Some prior art chairs have desirable features, such as stackability, or retention means for the reinforcement members. For example, U.S. Pat. No. 5,729,949, to Hartzheim discloses a readily stackable chair with a hollow-conical body that minimizes the amount of shipping and storage space required. This chair has support legs with apertures between them to allow concrete to flow into the hollow interior of the chair. A worker can carry many chairs at one time and place numerous chairs at a construction site without repeated trips to a storage area.
Some prior art chairs include retention means or clips for use in connecting reinforcing members together. U.S. Pat. No. 3,673,753 discloses a chair designed to have the reinforcing rod snap into a clamp and be securely maintained therein by hooks. The chair of U.S. Pat. No. 6,276,108 has a clip mounted on a post. The clip has a pair of orthogonal sockets for connecting reinforcement rods together at right angles to each other. Both of these patents disclose retention means which are designed for use with intersecting or crossing bars, and provide an attractive alternative to the wires which are widely used for tying reinforcing bars together. However, these prior art chairs are not able to be stacked, and therefore require an inordinate amount of space for shipping and storage.
While the prior art chairs described above fulfill their respective, particular objectives, a further need exists for a chair that is adapted to not only secure reliably the reinforcement members but also be stackable for more efficient shipping and storage. Also, a need exists for such a chair that has the strength and stability to withstand demanding and rigorous work loads.